Congenital anomalies are the second leading cause of perinatal mortality in the United States after premature birth. Advances in imaging techniques have allowed the detection of many anatomical defects with ultrasound before birth. The goal of this project is to improve the diagnosis and treatment of fetal disease and congenital anomalies. The Perinatology Research Branch has initiated a project to use three-dimensional ultrasound to delineate normal fetal anatomy, improve the detection of congenital anomalies and the estimation of fetal weight and growth. The diagnostic power of this technology is illustrated by the improved detection of cleft lip, vasa previa, and congenital anomalies. The findings of this year include the following: 1. Three-dimensional ultrasound was used to estimate fetal weight before birth. The fractional thigh volume obtained with the use of this technology was strongly correlated with birthweight (r=0.86). The best model to predict fetal weight used a combination of the abdominal circumference and fractional thigh volume. Our methodology resulted in estimations of fetal weight that had a 0.5% systematic error and 7% random error which compares favorably to the widely used model using conventional two-dimensional ultrasound (9% systematic error and 9% random error). 2. Three-dimensional multi-planar views of the fetal pelvis were used to standardize iliac angle measurements from normal second trimester fetuses, as well as a group affected by trisomy 21. The mean axial angle for normal fetuses was 79 (SD=5.5) degrees which was significantly less than observed in fetuses with trisomy 21 (mean=87; SD=4.9 degrees). Iliac angles did not correlate with gestational age. Angle measurements were reproducible where those obtained by coronal views were not. An axial angle of 87 degrees correctly identified 56% of fetuses with trisomy 21 with a false positive rate of 5%. 3. The Branch conducted a study to determine whether genetic ultrasound, in patients at moderate risk for trisomy 21 (1:190 to 1:1,000) based on triple-marker screening, was cost effective. We found that in women less than 35 years of age, a "genetic sonogram" improves the detection rate of Trisomy 21, is cost effective, and reduced the number of amniocenteses required to detect a fetus affected by this condition.